In recent years, there has been an increased interest in the use of alcohols, and in particular, methanol and ethanol, as a fuel for operating internal combustion engines. The early interest in alcohol powered internal combustion engines resulted from the shortages or threatened shortages such as occurred in the 1970's. However, when the threat of a shortage diminished, the automotive companies reduced their efforts to find alternative fuels which required changes in the design of engines to permit the engines to operate on alcohol fuel.
Internal combustion engines which can operate on both gasoline and alcohol, the so-called "flexible-fuel" or "variable-fuel" vehicles are particularly desirable since it may not always be possible, especially during an interim or changeover period, of finding service stations selling alcohol fuels If only gasoline is available in a particular area, the vehicle must be capable of performing with gasoline as well as alcohol
Attempts to substitute alcohol for gasoline as a fuel for internal combustion engines results in a variety of problems. Methanol has 40% less energy than gasoline, and, therefore, the miles per gallon obtained with methanol will be reduced by about 40% thereby requiring the vehicles to have larger fuel tanks. The automotive manufacturers also must design engines which take into consideration the fact that methanol is much more corrosive than gasoline. Not only does the fuel tank need to be made of corrosion-resistant materials such as stainless steel, the entire fuel delivery system has to be engineered with corrosion-resistant materials.
It also has been observed that when engines are operated with methanol as a fuel, corrosive wear and pre-ignition problems are often observed due to the presence of hot spots and the formation of ash deposits in the combustion chamber.
Although a number of the above-described problems and others which result from the use of alcohol fuels in internal combustion engines can be and are being resolved by optimization of internal engine components and by the use of new component technology such as electronic controls, modification of the lubricating oil compositions used to lubricate such engines is desirable. For example, efforts are underway to modify existing lubricating oils or to develop new lubricating oil formulations which are particularly useful in alcohol-fueled internal combustion engines, and when used in alcohol-powered internal combustion engines will prevent or minimize the pre-ignition and corrosion problems At the present time, it is further desired that the lubricating oil composition which is useful in an alcohol-fueled spark-ignited engine be also useful in lubricating gasoline-fueled, spark-ignited engines.